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ABS doesn't reduce fatalities, report by NHTSA discovers

Sep 01, 2009

Antilock braking systems (ABS) have close to a zero net effect on fatal crash involvements, according to a report by the National Highway Traffic Safety Administration (NHTSA).

NHTSA's Technical Report on the Long-Term Effect of ABS in Passenger Cars and Light Trucks and Vans (LTVs) is a statistical analysis based on data for calendar years 1995 to 2007 from the Fatality Analysis Reporting System (FARS) and the General Estimates System (GES) of the National Automotive Sampling System (NASS). The report's conclusions:

The long-term overall effect of ABS on fatal crash involvements is close to zero in both cars and LTVs. The observed effect in cars is a 1% reduction (90% confidence bounds range from a 2% increase to a 4% reduction). The observed effect in LTVs is a 1% increase (confidence bounds: -6% to 4%).

But the overall effect of ABS on all crash involvements, including nonfatal involvements is beneficial and statistically significant in both cars and LTVs. The observed reductions are 6% in cars (confidence bounds: 4% to 8%) and 8% in LTVs (confidence bounds: 3% to 11%).

The overall reduction of nonfatal-injury crashes is approximately the same as the reduction of all crashes.

Fatal run-off-road crashes increase with ABS by a statistically significant 9% in cars (confidence bounds: 3% to 15% increase). The long-term effect is substantially smaller than in the early years of ABS (28% increase), but it is still a significant increase. The observed effect in LTVs is a non-significant 6% increase (confidence bounds: -16% to 3%).

On wet, snowy, or icy roads, where ABS is most likely to activate, the increase in fatal run-off-road crashes is a statistically significant 34% in passenger cars (confidence bounds: 20% to 50% increase). On these roads, all three types of fatal run-off-road crashes increase significantly for cars and so do fatal rollovers of LTVs.

Side impacts with fixed objects generally increase even more with ABS than other types of run-off-road crashes (except for LTV fatalities). Fatal and nonfatal crashes both increase significantly for passenger cars.

The statistical analyses continue to show persistent, significant increases in run-off-road crashes with ABS, especially on wet roads. They remain at odds with the impressive performance of ABS on the test track, especially on wet roads. They do not tally with the benefits of ABS observed in other types of crashes. We are still unable to provide a convincing explanation or empirical evidence (other than the crash statistics themselves) for the increase in run-off-road crashes.

Fatal collisions with pedestrians, bicyclists, or animals decrease significantly, overall, with ABS. The observed reductions are 13% in cars (confidence bounds: 5% to 20%) and 14% in LTVs (confidence bounds: 3% to 25%). But the observed effects on wet, snowy, or icy roads are not positive.

Fatal run-off-road crashes of passenger cars increased by a statistically significant 9% (90% confidence bounds: 3% to 15% increase), offset by a 13% reduction in fatal collisions with pedestrians (confidence bounds: 5% to 20%) and a 12% reduction in collisions with other vehicles on wet roads (confidence bounds: 3% to 20%). ABS is quite effective in nonfatal crashes, reducing the overall crash involvement rate by 6% in passenger cars (confidence bounds: 4% to 8%) and by 8% in LTVs (confidence bounds: 3% to 11%).